This application claims the priority of German patent document 199 08 099.2, filed Feb. 25, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fuel cell system with an anode chamber and a cathode chamber separated from one another by a proton-conducting membrane.
At the present time, the reformation of methanol in a gas generating system is used for running liquid energy carriers through fuel cell systems with proton exchange membranes (PEM fuel cells) throughout the world. In this process, a water/methanol mixture is evaporated and reacted in a reformer to form hydrogen, carbon dioxide, and carbon monoxide. Evaporation and reformation are very expensive as far as energy conversion is concerned, degrading efficiency for the total system. In addition, gas preparation steps are required to purify the reformation gas. The purified gas is then supplied to the PEM fuel cell system.
In systems that use water for reformation, the product water on the cathode does not suffice to cover the water requirement, so that a separate water tank is necessary.
A fuel cell system of the type described above, containing a liquid fuel/coolant mixture is disclosed in German patent document DE 197 01 560 A1. A gas separator for separating carbon dioxide from the fuel/coolant mixture and a circulating pump are provided in the anode circuit, as well as a device for metering fuel into the anode circulation. A cooler is provided in the separated gas flow downstream from another gas separator. The coolant offgas from the known fuel cell system, which contains oxygen and water vapor, is conducted through a water separator and the separated water is fed into the anode circulation.
One object of the invention is to provide a PEM fuel cell system which achieves improved overall efficiency.
This and other objects and advantages are achieved by the fuel cell system according to the invention, in which an anode chamber and a cathode chamber are separated from one another by a proton-conducting membrane, with a cathode supply line for supplying gas containing oxygen to the cathode chamber and an anode supply line for supplying a liquid coolant/fuel mixture to the anode chamber. The anode chamber is located in an anode circuit that includes a gas separator and a pump, and a cooler and a water separator are located in the separated gas flow from the gas separator in the flow direction. According to the invention, the anode circuit has an operating pressure of at least 2.5 bars. The cooler is also cooled by a medium at ambient temperature.
By operating the anode circuit according to the invention at an operating pressure of at least 2.5 bars and by charging the cooler with a medium at ambient temperature, and the maximum temperature drop produced thereby, a maximum amount of water or fuel is recovered from the hot vapor-rich anode offgas, optimizing the total efficiency of the fuel cell system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.